Application Focus: Push-to-Talk (PTT)

Nick Fox Application Focus, General, How-to

Application Focus

In this new series we shall highlight some of the applications of the MultiDSLA system. The aim is to build a concise and practical guide to the many applications in which MultiDSLA delivers reference measurements around the world.
We begin with the subject of Push-to-Talk.

Why Push-to-Talk?

Push-to-Talk, often referred to as PTT, is a form of wireless voice communication in which only one direction of communication is open at a time.  The person speaking must first operate a PTT button (or key, footswitch, touch-screen, voice-operated switch, etc.) to open the communication path.  PTT services are used by first responders, the military, fleet operators, in warehouses, the construction industry and many more.  Like other types of phone calls, PTT calls may be one-to-one, but unlike other types of call may also be one-to-many, often referred to as a ‘group call’.

Standards

PTT standards include Project 25 (P. 25) in North America and TETRA and TETRAPOL in Europe, although all of these have international applications. Equipment manufacturers include Motorola, Midland, Kenwood, Icom, Tait, Sepura and Airbus DS.

Equipment consists of hand-held terminals (‘personal radios’, ‘walkie-talkies’), vehicle-mounted terminals (‘mobiles’, ‘vehicle radios’), control room terminals (‘dispatcher terminals’, ‘control terminals’) and base stations (‘fixed’ transmitters and receivers).

 

Some cellular network operators have offered ‘PTT-over-cellular’ services (PTToC), leveraging the capacity and economics of commercial networks to deliver value-added services to industrial customers.  This provides a communications service to those customers without them having to operate their own radio networks.

A transition is taking place in some markets, from the standards mentioned above to those based on 4G/LTE cellular networks.  Numerous manufacturers already produce ruggedized cellular phones and the associated accessories, and these will eventually replace at least some of the legacy terminals.

Characteristics of PTT services

 

  • ‘One-to-one’ or ‘one-to-many’ communications
  • Rapid call setup
  • No need to answer the call
  • A more job-focused ‘etiquette’ for calls

Who uses MultiDSLA for PTT application testing?

Categories of customer using MultiDSLA to test PTT system and terminal performance include:

  • Cellular operators
  • Chipset vendors
  • Mobile and portable terminal manufacturers
  • Dispatcher console manufacturers
  • TETRA network operators
  • TETRAPOL network operators
  • Police forces
  • Tactical communications manufacturers
  • PTT app developers for LTE

How does MultiDSLA help?

One of the challenges in assessing PTT services is the need to operate the push-to-talk button before testing the performance of a voice signal.  The DSLA Control Line solves this problem by operating the PTT automatically, at the right time and for the right duration.  A typical tasklist (test sequence) for a two-way call looks like this:

 

This test essentially does what one of the standard MultiDSLA tests does, but also performs the PTT operations at each end of the test call.  Using this tasklist, we obtain POLQA and PESQ scores and one-way latency/delay, as for most other types of call.  But there may be additional requirements for PTT, because one of the key performance indicators (KPI) – particularly in the evolving 4G cellular environment – is call setup time.  The caller operates the PTT and typically waits to hear a pip tone.  This is the confirmation that the voice path is open and that he/she may begin to speak.  MultiDSLA can not only identify the pip tone but also measure how it long it takes to arrive after the PTT is activated:

Some users may also need to measure the release-to-tone time, which is the time between releasing the PTT until receipt of a tone confirming that the speech path has been closed.

Custom Tests

Users find it simple to generate custom tests for many types of measurement, and those having Maintenance Cover for their test system may also request a template to give them a head start, by writing to Support@OpaleSystems.com.